There is an ever increasing demand for low cost, accurate weighing systems for use on load bearing vehicles such as portable grain feed mixers and mills employed by the farming industry. Weighing systems for such vehicles must be extremely rugged and capable of operating effectively after being exposed to the shock and abuse presented by the environment in which farm vehicles operate. Such vehicles are normally operated over rough terrain and are exposed to the elements including extremes of temperature and humidity.
Although electronic weighing systems employing gauge technology have long been known to the art and are readily available, such devices are not readily adapted for use in a rough vehicular environment. On board electronic weighing systems have found widespread use on vehicles normally operated over roads or other flat surfaces, but these vehicular weighing systems are not subjected to the variations caused by uneven terrain, where operation on inclines and over rocks and crevices induces numerous measurement errors.
Recently, attempts have been made with some success to develop simple, economical, and accurate electro-mechanical weighing systems for rugged vehicular use. Examplary of such systems are the strain gauge weighing device and the vehicle coupling weighing device disclosed by U.S. Pat. Nos. 3,650,340 and 3,669,756 to Richard S. Bradley.
The Bradley weighing system for vehicles provides a measurement which is substantially independent of the mounting surface upon which the vehicle rests. The two pairs of electrical resistance strain gauges are affixed to each vehicle load member with each pair having one strain gauge mounted above and the second strain gauge mounted below the load bearing member in juxtaposition. The strain gauges of each pair are affixed to the load member, and the first pair of strain gauges is spaced a prescribed distance from the second pair. The strain gauges provide inputs to microminiature integrated circuitry which is housed in a remotely located housing.
The load members employed in the Bradley system constitute replaceable vehicle axles, and no modification of the vehicle is required other than the substitution of a replaceable axle and axle mounting plate. This replaceable axle is a stub axle which is rigidly connected to the load receiving container.
Although the weight measuring system of the Bradley patents provides definite advantages over prior systems for rugged vehicular use, this system is still subject to certain deficiencies when employed on load carrying vehicles. For example, the Bradley strain gauge weighing device requires the use of at least four strain gauges disposed in horizontal spaced relationship with one strain gauge of each pair being affixed to the upper surface of an axle while the remaining strain gauge of each pair is affixed to the lower surface of an axle. The upper and lower strain gauges must be mounted in juxtaposition, and the pairs of strain gauges must be spaced one from another on the axle surface. This surface mounting of the strain gauges in relatively widely spaced relationship on the axle of a load bearing vehicle adapted for rugged use makes it very difficult to protect the gauge units from damage. It is necessary to provide a protective covering sufficient to include both spaced pairs of strain gauges, but since the gauges are externally mounted on the axle, even a protective covering is insufficient to shield the gauges from shocks imposed by rocks and other objects which strike the axle.
For the spaced strain gauge pairs illustrated in the Bradley patent to operate effectively to measure differential bending these gauges must be mounted very near the upper and lower surfaces of the supporting axle, and threfore even if the gauges are slightly embedded in the axle surface, they are still very difficult to protect. In actuality, such embedded gauges are still the full equivalent of surface mounted gauges and are responsive to external temperatures and humidity adjacent the surface of the axle. Also, embedded gauges are still subjected to severe shock received by the axle surface, and are much more likely to be damaged by water and other elements which might be admitted by a defective or worn out protective covering.
Ideally, the axle mounted strain gauges should be placed centrally within the axle, but this often results in severe weakening of the axle structure. Exemplary of such weakened structures is the force transducer shown by U.S. Pat. No. 3,602,866 to Erwin J. Saxl. Here a lead carrying beam is formed with a reduced waist section, and a hole for receiving strain gauges is then formed in this reduced waist section.
It is a primary object of the present invention to provide a novel and improved vehicle weighing device wherein sensing gauges are applied to separate stub axles and a hitch unit for the vehicle. However, these gauges are mounted internally within the stub axle or hitch to which they are affixed, and are therefore as far removed as possible from the outer surfaces thereof. This enables the gauges to be completely protected from the elements and from shocks to which the gauge bearing member is subjected.
Another object of the present invention is to provide a novel and improved vehicle weighing system which operates effectively with the minimum number of active weight sensing units. On any stub axle or vehicle coupling arm bearing a sensing gauge assembly, only one pair of active gauges is required. The individual gauges in this active pair of gauges are mounted in closely spaced relationship, and therefore are much easier to protect from shock and the effects of the elements than widely spaced gauge pairs presently employed in known vehicle weighing systems. Also, the use of only two active gauges greatly reduces the cost of the gauging system.
A further object of the present invention is to provide a novel and improved vehicle weighing system wherein measuring gauges are mounted on separate axle units and a hitch for the vehicle. The gauges affixed to each axle unit and hitch are mounted within a hole oriented perpendicular to the direction of load to retain maximum fiber strength for the mounting unit. The gauges are angularly oriented to measure strain, thereby producing a high output without requiring a reduction in the cross section of the gauge bearing member adjacent the gauges. Temperature tracking may be effectively provided by two gauges located on the neutral axis of a load bearing member and oriented cross-wise to the direction of loading so that they will be subjected to no strain.
A still further object of the present invention is to provide a novel and improved vehicle weighing system wherein both sensing gauges and the bridge circuitry for such gauges is mounted in close relationship directly on a load bearing member.